Plasma amino acid levels were measured in autistic (n=12), Asperger syndrome (n=11) patients, their parents and siblings. Patients with autism or Asperger syndrome and their siblings and parents all had raised glutamic acid, phenyalanine, asparagine, tyrosine, alanine, and lysine levels than age-matched controls. Results suggest dysregulated amino acid metabolism as an underlying biochemical basis. (Contains references.) (Author/DB)